Laser surgical cutting probe and system

ABSTRACT

A surgical laser system combines a laser diode array remotely connected to a hand-held surgical probe by a fiber bundle. The surgical system has a which includes a laser head which produces a laser beam for surgical tissue ablation that is delivered through a disposable intraocular probe tip. The probe tip is made of a short section of optical fiber. Preferably, the laser head is an Er:YAG rod pumped by energy from the laser diode array to operate at a wavelength of 2.94 microns. Auxiliary water and thermal electric cooling integral to the hand piece cools the laser head.

BACKGROUND OF THE INVENTION

The present invention relates generally to laser cutting probes for usein surgical procedures. More particularly, this invention pertains to asolid-state erbium laser surgical cutting probe and system for use insurgical procedures requiring high precision, including intraocularsurgical procedures such as retinotomy, vitrectomy, retinectomy,capsulotomy, sclerostomy, and goniotomy.

Laser cutting, ablation and vaporization are common techniques insurgery. For example, the CO₂ laser has been used in dermatology forcutting tumors. Corneal cutting and reshaping is being performed withexcimer photorefractive surgery (PRK). The best laser wavelength formany procedures is the wavelength having the highest absorption intissue. Because water comprises the highest component of the tissue, thebest water absorption wavelength often has the best cutting effect.

The most commonly used lasers for cutting are CO₂ laser at 10.6 μm(water absorption coefficient=8.5×10²/cm⁻¹), and Er:YAG at 2.94 μm,(water absorption coefficient=1.3×10⁴/cm⁻¹).

Intraocular cutting techniques are needed for ophthalmic surgery. Laserintraocular cutting may improve the surgery with smaller incisions,easier control, and higher precision. Several studies have trieddifferent lasers and various delivery devices to develop this technique.

Lewis A. et al. in the Hebrew University of Jerusalem, Israel, guided anexcimer laser beam (193 nm) with an articulated mechanical arm andconfined it with a variable-diameter tapered tube (1 mm to 125 μm indiameter). An air stream was used to push the intraocular liquid out ofa cannula and remove fluid from the retina surface just in front of theneedle tip. With such an excimer laser delivery system, it was possibleto remove retinal tissue accurately without collateral damage.

Dodick J M, et al tried to overcome the delivery problems by conductinga short pulse Nd:YAG laser (1.064 μm) into the eye with a silica fiber.At the end of the surgical probe, the short pulses hit a titanium targetand generated shock waves. This device was applied to fragment nuclearmaterial for cataract extraction.

D'Amico et al delivered Er:YAG laser through a fluoride glass fiber toan endoprobe with sapphire or silica fiber tips ranging from 75 to 375μm. This probe was used for transection of vitreous membranes,retinotomy, and incision and ablation of epiretinal membranes. Resultsshowed that twenty-five vitreous membrane transections were made in 16eyes at distances ranging from 0.5 to 4.5 mm from the retina withradiant exposures ranging from 2 to 50 J/cm2 (0.3-5.5 mJ) withnonhemorrhagic retinal damage in a single transection. Sharp, linearretinotomies were created successfully in five eyes. Epiretinal membraneablations were performed with radiant exposures ranging from 1.8 to 22.6J/cm2 (0.3-2 mJ). In aqueous media, results of microscopic examinationshowed partial- to full -thickness ablation with a maximum lateralthermal damage of 50 μm. In air- and perfluoro-N-octane-filled eyes,there was increased lateral damage with desiccation of residual tissue.In 12 aqueous-filled eyes, 18 linear incisions were successfullyperformed, with retinal nonhemorrhagic damage in 2 eyes and hemorrhagein 5. Based on these results, a commercial florid glass delivered Er:YAGlaser has been developed for further research (VersaPulse®Select™Erbium, Coherent®, Palo Alto, Calif.).

Joos K, et al delivered Er:YAG laser (2.94 μm) through ZrF fiber andcoupled to a short piece of sapphire fiber (Saphikon, Inc., Milford,N.H.), or low-OH silica fiber at the end of the intraocular probe. Theprobe was combined with an endoscope to perform goniotomy in vitro andin vivo. The results showed that minimum tissue damage created with theEr:YAG energy was at an energy level of 2 to 5 mJ per pulse.

Pulsed Er:YAG laser at 2.94 μm wavelength is capable of cutting humantissue with high precision and little thermal damage to the surroundingtissue. The potential applications include photo-refractive keratectomy,plastic surgery, and intraocular cutting surgery such as retinotomy,vitrectomy, capsulotomy, goniotomy, etc.

To understand the proper use operation of a micro-Er:YAG laser in thesurgical applications, it is important to understand its dynamics. Theenergy level scheme of a 970 nm diode pumped Er³⁺ in a YAG crystal isshown in FIG. 4. The 970 nm diode directly pumps the Er³⁺ to the upperlaser energy level. The laser action occurs between the⁴I_(11/2)-⁴I_(13/2) states. Each of these states is Stark split intoabout 6 to 7 branch energy levels by the crystal field. These levels arethermally populated as described by a Boltzmann distribution. When theX2 branch of ⁴I_(11/2) is relatively higher populated than the Y7 branchof ⁴I_(13/2), the 2.94 μm laser transition will occur, even when theentire ⁴I_(11/2) and ⁴I_(13/2) levels are not inversed. Continuous wave(CW) and quasi-cw laser operations of this transition atroom-temperature have been reported with high efficiency and high outputpower. When the population of ⁴I_(13/2) accumulates to a certaindensity, two neighboring Er³⁺ ions can interact. One ion jumps to thehigher energy ⁴I_(9/2) and the other one jumps to the lower level⁴I_(15/2). Then the ⁴I_(9/2) level ion will relax to the upper laserlevel ⁴I_(11/2) by rapid multi-photon transition within about 1 μs. Thisis called the up-conversion process. It is responsible for shorteningthe lifetime at the lower laser level which simultaneously leads toexcitation of the upper laser level.

Since lifetime at the ⁴I_(11/2) level is shorter than at the ⁴I_(13/2)level, highly doped crystals such as YAG:Er³⁺ at 50% concentration haveto be used to reduce the lifetime at the lower laser levels, andincrease the probability of interaction at the lower level laser ions

All commercial Er:YAG lasers presently are flash light pumped. Some ofthe companies which produce the Er:YAG lasers are: Big Sky, SEO, LSD,Kigre, FOTONA, Quantex, etc. The most common feature of these lasersare: wavelength—2.94 μm; pulse length—150 to 300 μs; energy perpulse—100 to 1000 mJ; and repetition rate—1 to 20 Hz.

Other manufacturers (e.g. Coherent, Premier, and Candela) producefluoride glass delivered Er:YAG laser. Because all fluoride glass fiberscan not withstand high laser power, these lasers normally have outputsof less than 20 mJ per pulse of energy.

Kigre Inc. produces a small Er:YAG laser, which places a small flashlight pumped Er:YAG laser head into a pistol style hand piece. However,it requires high voltage power for the flash light and the hand piece isnot small enough for intraocular surgery.

There is no commercialized diode pumped Er:YAG laser. Theoretical andpreliminary experiments showed that a diode pumped Er:YAG laser has amuch higher conversion efficiency (10% to 20%) than flash light pumpedones (efficiency <2%). Dinerman, et. al. used a 970 nm diode laser and aTi:sapphire laser to end pump a 3 mm long Er:YAG laser. This produced143 mW of cw power when the pump power was 718 mW. Hamilton, et. al.pumped a 2×2×14 mm Er:YAG laser rod with a pulsed diode laser array barwith 200 W peak power, and reached the maximum output energy of 7.1 mJper pulse at 100 Hz repetition rate. The parameters and results of theseexperiments are listed in Table I:

TABLE 1 Previous experiments of diode pumped Er:YAG lasers Er:YAG #1Er:YAG #2 Er:YAG #3 Pump wavelength: 970 nm 963 nm 963 nm source Max.peak 718 mW 200 W 200 W para- power: 88 mJ 88 mJ meters: Max. pulse cw400 μs 400 μs energy: pulse length: Er:YAG rod size: Φ3 × 3 mm 2 × 2 ×14 mm 1 × 1 × 14 mm laser Er³⁺ 33% 50% 50% para- concentration: 3 mm 40mm 25 mm meters: cavity length: 99.7% 98% 98% output coupler: Outputpump 410 mW results: threshold: total efficiency: 8% 5.3% slope 12% 13%efficiency: Max. peak 171 mW 17 W 11.75 W power: 7.1 mJ 47 mJ Max. pulsecw 100 Hz 275 Hz energy: repetition rate:

These results indicate that using a diode array pumped micro-Er:YAGlaser is very promising for low energy requirements.

One of the biggest difficulties in the practical application of theerbium laser for such surgical applications is that none of theavailable fibers are ideal for the delivery of the laser. In addition tothe bulky mechanical articulated arm, fiber optics available for thesewavelengths are: fluoride glass fiber, single-crystal sapphire fiber,chalcogenide glass fiber, polycrystalline fiber, and hollow waveguides.Although they offer some ability to deliver different cuttingwavelength, all of them have one or more defects of: brittleness, watersolubility, toxicity, sensitive to UV exposure, limited mechanicalstrength, low temperature damage threshold, and low laser damagethreshold. The articulated arms and sapphire fibers are not flexibleenough for effective use by the surgeon. Although fluoride glass fibershave better flexibility, they are too brittle and their damage energythresholds are too low for intraocular use.

What is needed, then, is a cutting probe system that is sufficientlyflexible and mechanically strong to reliably deliver the energy from anerbium laser for use in intraocular surgery and in other surgicalprocedures requiring high precision.

SUMMARY OF THE INVENTION

The shortcomings of the prior art have been addressed in this inventionby a novel micro Er:YAG laser (2.94 μm) based intraocular surgical probesystem.

To avoid the difficulty of fiber delivery of the erbium laser power, thesystem includes an erbium laser head which fits into a surgical handpiece. The output of the erbium laser from the hand piece is deliveredto the surgical field by a short piece of rigid sapphire or low-OHsilica fiber which forms a disposable probe tip. The erbium laser headis pumped by diode laser energy delivered by a silica fiber bundle,instead of a high voltage electric powered flash lamp, so that the handpiece is safe and easy to hold.

The probe uses a plug-in style disposable tip which is made of a shortpiece of silica or sapphire fiber. This probe is capable of delivering arange of 0.5-10 mJ per pulse of 2.94 μm laser energy at approximately at1-20 Hz. Accordingly, the probe and system can be used to performvitreoretinal surgery, including retinotomy, vitrectomy, capsulotomy,goniotomy, as well as other superficial surgery where precise tissuecutting is necessary. With an enlarged erbium laser head, the cuttingprobe of this invention can produce enough energy to perform lasercataract removal.

The laser cutting probe and system of this invention solves thedifficulty of delivering Er:YAG laser energy at 2.94 μm. It rendersintraocular cutting clinically possible with a laser and may be usefulalso in other subspecialties which need low energy levels and precisetissue cutting.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a preferred embodiment of the erbium lasersurgical system of this invention.

FIGS. 2a, 2 b, and 2 c are cutaway side views showing positioning of theprobe of the system of FIG. 1 during a) retinotomy; b) cutting ofvitreous bands; and c) goniotomy.

FIG. 3 is a graphical representation showing the level of energyabsorption in water as a function of laser wavelength.

FIG. 4 is a graphical representation of the energy level of a 970 nmdiode pumped Er in a YAG crystal.

FIG. 5 is a side view of a first embodiment of the laser head used inthe system of FIG. 1, in which a side pump configuration is used.

FIG. 6 is a is a side view of a second embodiment of the laser head usedin the system of FIG. 1, in which an end pump configuration is used

FIG. 7 is an enlarged oblique view of the diode laser array used in thesystem of FIG. 1.

FIG. 8 is an enlarged side view showing the coupling of the output fromdiode laser array of FIG. 7 into the silica fiber bundle of FIG. 1.

FIG. 9 is an enlarged cutaway side view of the surgical hand piece ofthe system of FIG. 1.

FIG. 10 is an enlarged side view of another embodiment of the disposabletip of FIGS. 1 and 9, showing an infusion/suction line.

FIGS. 11a and 11 b are perspective views of two configurations of Er:YAGlaser rods used in the system of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The novel laser surgical laser cutting system 10 of the presentinvention is shown in FIG. 1, in which a laser energy source 11 iscoupled to a surgical probe assembly 12 by a remote connect assembly 13.The laser energy source 11 preferably combines a diode laser array 14with a matching power supply 15. The output of the laser diode array 14passes first through a column lens 16 and then through a focusing lens17 which directs the laser energy into the input end of a fiber bundle25 (FIG. 8) as part of remote connect assembly 13.

The novel surgical probe assembly 12 has a hand piece 18 which holds aninternal laser head 19. Preferably, the laser head 19 uses a solid-statelaser medium such as an erbium-doped yttrium aluminum garnet rod orcrystal (Er:YAG). The laser head 19 is connected to the output end offiber bundle 25. Accordingly, the Er:YAG laser head 19, when pumped bythe diode laser energy from the laser energy source 11, will generateand deliver laser radiation at a wavelength of 2.94 microns to andthrough a disposable probe tip 20.

FIG. 9 provides additional detail about the novel design of the probeassembly 12. The surgical hand piece 18 is sized and shaped to fiteasily into the hand of the surgeon. For example, a hand piece 18 havingan outside diameter of approximately 15 mm, and length of about 10 to 15cm, should accommodate the needs of most users. To provide strength,durability, heat dispersion, and ease of sterilization, the hand piece18 is preferably made of stainless steel or a titanium alloy.

As best seen in view (a) of FIG. 9, the hand piece 18 includes a sealedchamber 21 which supports the micro Er:YAG laser head 19 (FIG. 9(b)) andisolates it from moisture and dust.

So that the probe assembly 12 can be effectively used in delicateintraocular surgery, a visible aiming beam should be combined with the2.94 μm cutting laser in the probe tip 20. Accordingly, a visible aimingbeam is generated externally and delivered to the hand piece 18 via amulti-mode optical fiber 22 as part of remote connect assembly 13. Theoptical fiber 22 enters the hand piece 18 and is positioned adjacent tothe Er:YAG head 19 to deliver the aiming beam through the probe tip 20.As best seen in FIGS. 5 and 6, a sapphire or CaF₂ hemisphere ball lens23 is aligned transversely across the output end of the hand piece 18and laser head 19. The lens 23 seals the chamber 21 and focuses theoutput of the laser head 19 into the probe tip 20. The lens 23 ispreferably coated with anti-reflection film at 2.94 μm and will alsofocus some of the visible light from the aiming beam fiber 22 into theprobe tip fiber 20. Therefore, the aiming beam output will be parallelto the 2.94 μm laser Er:YAG output, making it useful to the surgeon inmanipulation of the hand piece 18. Because the Er:YAG laser head 19itself forms the laser cavity, no special optical alignment is needed. AHeNe laser (not shown) coupled to a 200 μm diameter fiber 22 can be usedto generate the aiming beam.

The Er:YAG laser head 19 generates heat that should be dissipated toavoid overheating of the hand piece 18. To address this need, coolingwater is delivered to and circulated around the interior of hand piece18 by a cooling channel 24, to remove the thermal load from the laserhead 19. External to the hand piece 18, the cooling channel 24 is formedof two thin silicone tubes integrated into the remote connect assembly13, one to deliver the water and one to return the water to a miniaturewater pump (not shown). To provide temperature monitoring for safetypurposes, a temperature sensor, such as a thermocouple (not shown), canbe positioned inside the hand piece 18. The output of the temperaturesensor is sent to an external temperature monitor (not shown) throughelectrical wire cable 26, which can be part of the remote connectassembly 13. Preferably, the temperature monitor will have an overheatsetpoint that will generate a shut down signal to the laser energysource 11 if an overheat condition occurs.

The overall size of the chamber 21 and laser head 19 should be in therange of 10 mm in diameter, and less than 50 mm in length, so that itwill fit into the hand piece 18. FIGS. 5 and 6 show two differentconfigurations for the components internal to the hand piece 18. FIG. 5illustrates a side pump arrangement in which the individual fibers inthe pump light fiber bundle 25 (forming part of connect assembly 13)enter and deliver the pumped laser energy from the laser diode array 14(FIG. 1) into the sides of laser head 19. In the side pumpconfiguration, the preferred dimensions of the Er:YAG laser rod whichforms laser head 19 will be 1×1×10 mm. The Er³⁺ concentration will be50%. At this doping level, and using a 970 nm diode laser pump light,the transmission depth in the crystal is ˜1 mm. As seen in FIG. 11(a),the ends of the Er:YAG rod will be coated with (2.94 μm wavelength) 100%high reflective and 98% reflective mirror respectively. The highreflective (HR) end of the rod 19 will have a radius of 30 mm and the98% reflective output coupler 26 will be flat so the Er:YAG rod 19itself will form a stable oscillator cavity. The two sides which contactthe pump fibers 25 will be coated with anti-reflective material at 970nm wavelength.

In the configuration of FIG. 6, the pumped laser energy is delivered tothe end of the Er:YAG laser head 19. As shown in FIG. 11(b), the Er:YAGlaser rod 19 is preferably 3×3×3 mm for the end pump configuration, withan Er³⁺ concentration of 30% for a deeper transmission of pump light.The laser oscillator cavity also will be formed by the two ends of thecrystal rod. The end of the head 19 which contacts the pump light fiberbundle 25 will be HR at 2.94 μm, anti-reflective (AR) at 970 nm, andflat. The output coupler 26 will have 99% reflectivity at 2.94 μm, HR at970 nm, and have a radius of 30 mm.

The Er:YAG rods 19 as shown in FIGS. 5, 6, and 11 can be obtained fromScientific Materials Corp., Bozeman, Mont.

Instead of using a high voltage powered flash lamp as a pump source, thelaser head 19 of the system 10 is pumped by a fiber bundle deliveredInGaAs diode laser array at 970 nm wavelength. FIG. 7 is an enlargedview of a typical SDL InGaAs diode laser array 14. The diode laser arraymodel SDL-6231-A6 from SDL, Inc.(970 nm central wavelength) is an ideapump source 14. The SDL InGaAs diode laser array 14 is made up of sixone dimensional diode bars, which have an illumination area of 10 mm×1μm. The bars are bonded to separate microchannel cooling packages,which, on being stacked to form the array, result in a diode bar spacingof 400 μm.

The diode array 14 as shown can produce a 400 μs pulse with up to 360 Wpeak power at a repetition rate of up to 50 Hz. Considering a pump rateat which 70% of total pump energy is delivered to the Er:YAG rod 19, theEr:YAG laser head 19 can generate 10 mJ per pulse of energy. At 20 Hzrepetition rate, the average output power of the diode laser array 14 is2.88 W. To remove this amount of thermal load in the Er:YAG head 19,auxiliary thermal electric heating panels 27 are positioned inside handpiece 18 immediately above and below the laser head 19. The panels 27,which are conventional in design and operation, are connected to anexternal low voltage supply through electric cable 26. Coating thethermal electric cooling plates 27 with metal may be necessary forbetter thermal conduction. The thermal exchange rate of the thermalelectric cooling plates 27 (FIGS. 5 and 6) should exceed the averageoutput power of array 14. Such a device is commercially available. Themodel CP 1.4-3-045L from Melcor Corp. (Trenton, N.J.) has a maximum heatabsorption rate of 1.6 W per piece, with a size of 5×10×3.3 mm. TheEr:YAG rod 19 is sandwiched between two of these thermal electriccooling plates 27 which can provide up to 3.2 W maximum thermalabsorption rate.

FIG. 8 schematically shows the coupling of the diode laser array 14 intosilica fiber bundle 25. Two lenses are be used to couple the diode laseroutput into the fiber bundle 25. The first is a cylindrical column lens16, which captures the fast axis of the diode laser array bar andreduces the full-angle divergence close to the slow axis. The secondlens 17 focuses the diode laser beam onto the surface of the fiberbundle 25. Since the fiber bundle 25 has a total diameter ofapproximately 3 mm, such coupling is feasible. In order to increase thecoupling efficiency, all of the optical surfaces including the fiberbundle surface will be coated with anti-reflection film. A standard SMA905 connector can then be used to link the fiber bundle 25 to the 970 nmdiode laser source 14. The peak power of the pump light from the laserenergy source 11 should be greater than 200 W at a repetition rate of1-20 Hz.

The fiber bundle 25 can be fabricated from multiple 100 μm or 60 μm corediameter multimode silica fibers bundled for the pump light delivery.Silica fiber is very strong and flexible and is satisfactory for medicalapplications. The total diameter of the fiber bundle 25 is approximately3 mm. For the end pump configuration of FIG. 6, the fiber bundle 25 willnearly contact the HR end of the Er:YAG rod 19 (FIG. 11(b)).

For the side pump configuration of FIG. 5, the fibers of bundle 25 arebent 90 degrees under high temperature, and then the fibers are packedto a linear array. Both sides of the Er:YAG rod 19 are in contact withthe fiber array. The other ends of these two fiber arrays will bebundled together, and connected to the diode laser pump source 11. Theoutput of the laser head 19 should be 0-10 mJ at 1-20 Hz.

Accordingly, remote connect assembly 13 will preferably integrate (1)the pump light fiber bundle 25 from the diode laser array 14; (2) theelectrical cable 26 containing four thin electric wires of 0.36 voltageto power the thermal electric cooling plates 27 and to connect thetemperature sensor to the temperature detector, (3) the cooling channel24; and (4) the single multi-mode fiber 22 for the visible aiming beam.

The probe tip 20 of probe assembly 12 is a plug-in disposable tip whichis made of a short piece of silica or sapphire fiber having a diameterof 200 microns. This probe tip 20 is capable of delivering a range of0.5-10 mJ per pulse of 2.94 μm laser energy at approximately at 1-20 Hz.

As seen in FIG. 10, the disposable tip 20 can incorporate aninfusion/suction line 28 to aid in surgery. The infusion/suction line 28can be attached along the side of the hand piece 18 as shown in FIG.10(b) or passed through the inside of the hand piece 18. A conventionalphacoemulsification machine (not shown) can then be used by the surgicalteam to control irrigation/aspiration in the surgical field adjacent tothe probe tip 20. For example, FIGS. 2a, b, and c show intraocularpositioning of the probe tip 20 during retinotomy, cutting of vitreousbands, and goniotomy respectively.

Although a preferred embodiment of the system has been described for usein intraocular surgery, the probe and system of this invention can beadapted to a variety of different surgical procedures where a highdegree if precision is required.

Thus, although there have been described particular embodiments of thepresent invention of a new and useful Laser Surgical Cutting Probe andSystem, it is not intended that such references be construed aslimitations upon the scope of this invention except as set forth in thefollowing claims.

What is claimed is:
 1. A system for performing laser surgery comprising:a. a laser energy source remotely connected to a surgical probe assemblyby a remote connect assembly, the remote connect assembly including afiber bundle adapted to transmit laser pump energy from the laser energysource; b. the surgical probe assembly comprising a hand piece having asize and shape adapted for gripping, a chamber internal to the handpiece, the chamber enclosing a laser head, and a probe tip, the chamberbeing sealed against entry of moisture and dust; and c. the laser headoperatively coupled to the fiber bundle to receive the laser pump energywhereby the laser pump energy causes the laser head to generate a beamof laser radiation at a predetermined wavelength and energy level, thebeam of laser radiation optically coupled to and directed through theprobe tip, the fiber bundle having an output end that is closelyproximate to or in contact with an external coupling surface portion ofthe laser head, the output end of the fiber bundle coveringsubstantially all of the coupling surface portion of the laser head. 2.The system of claim 1 wherein the probe tip comprises a piece of opticalfiber removably attached to the hand piece whereby the probe tip can beseparated from the hand piece and laser head to be disposed of andreplaced after use.
 3. The system of claim 1 further comprising asuction/infusion line adapted for delivering and removing fluidsproximate the probe tip.
 4. The system of claim 1 wherein the fiberbundle comprises a plurality of bundled silica fibers.
 5. The system ofclaim 1 whereby the laser energy source comprises a diode laser arraygenerating the laser pump energy at a wavelength of 970 nm and the laserhead comprises an Er:YAG rod whereby the beam of laser radiation has awavelength of 2.94 microns.
 6. The system of claim 5, the laser energysource further comprising a column lens and a focusing lens aligned inan optical path between the laser diode array and the fiber bundle. 7.The system of claim 5 wherein the fiber bundle is side coupled to theEr:YAG rod.
 8. The system of claim 5 wherein the fiber bundle is endcoupled to the Er:YAG rod.
 9. The system of claim 5, the surgical probeassembly further comprising means to deliver a visible guide beamindicating the position of the beam of laser radiation.
 10. The systemof claim 1 wherein the surgical probe assembly further comprisesauxiliary cooling means integral to the hand piece.
 11. The system ofclaim 10, the auxiliary cooling means comprising a thermal electriccooler proximate the laser head.
 12. The system of claim 10, theauxiliary cooling means comprising a recirculating fluid channel. 13.The system of claim 1 wherein the laser head comprises a crystal rodhaving flat end portions forming an oscillator cavity.